1. Field of the Invention
The present invention relates to a method for sensor node roaming in a wireless sensor network environment, and more specifically, to a method for effective sensor node roaming between adjacent wireless sensor networks.
2. Discussion of Related Art
Generally, a wireless sensor network or a ubiquitous sensor network is a network of a plurality of sensors arranged to wirelessly collect and process various data sensed by the sensors to thereby transmit the sensed data to a manager
Compared to a general wireless mobile communication network, such a wireless sensor network has self-organizing ability, features of short range broadcast communication and multi-hop routing, densely deployed sensor nodes, cooperating sensor nodes, suddenly changing topology due to radio fading and sensor node failure, and limitations in energy consumption, transmission output, memory, and computing ability due to microminiaturized sensor node structure.
FIG. 1 is a conceptual diagram showing the configuration of a general wireless sensor network.
Referring to FIG. 1, a general wireless sensor network (WSN) is a kind of ad-hoc network composed of sensor nodes SN1 to SN5 (for example, ZigBee) and a sink node for particular purposes. In order to provide collected information to a user, the WSN employs a legacy network including an IP-based network (BcN). Thus, the collected information should be passed through a gateway.
Also, an application server (AS) is needed to provide various wireless sensor network-based application services. Each sensor node SN1 to SN5 has a sensing function for sensing peripheral information, a transmission function for transmitting it to another sensor node, and a reception function for receiving information transmitted from other sensor nodes.
Furthermore, although not illustrated in FIG. 1, there is a gateway for connecting existing wired and wireless telephone networks with the IP-based network.
FIG. 2 is a diagram showing movement of the sensor node of FIG. 1 from a current wireless sensor network to a neighboring wireless sensor network, and FIG. 3 is a flowchart showing the sensor node movement of FIG. 2.
Referring to FIG. 2, in the case where the sensor node SN1 with mobility in the existing wireless sensor network WSN1 moves to a neighboring wireless sensor network WSN2, the sensor node SN1 forms an association with its parent node in a medium access control (MAC) layer so that even though it moves to the neighboring wireless sensor network WSN2, it cannot perform communication in the wireless sensor network WSN2.
When the sensor node SN1 moves to the neighboring wireless sensor network WSN2 and then moves back to WSN1, it can again perform communication in WSN1.
In other words, a sensor node in a particular wireless sensor network can perform communication only in the particular wireless sensor network. If it moves to a neighboring wireless sensor network, it cannot perform communication there.
Referring to FIG. 3, the mobile sensor node SN1 in the wireless sensor network WSN1 should form an association with its parent node PN1 in order to transmit data in the wireless sensor network WSN1. In order to judge if there is a certain node where the sensor node is positioned before forming such an association, a routine is needed for judging if there are certain nodes in the vicinity and if the sensor node should form an association with a certain node, through an active scan or a passive scan. Through such a process, an environment enabling the sensor node N1 to perform data communication in the wireless sensor network WSN1 is provided.
When the sensor node SN1 does not perform data communication with its parent node PN1 or other sensor nodes SN2 to SN5 in its wireless sensor network WSN1, but moves to neighboring wireless sensor network WSN2, it cannot perform communication if it is out of radio frequency communication range from its parent node PN1 and the sensor nodes SN2 to SN5 in the wireless sensor network WSN1. Consequently, it is unknown whether there is the sensor node SN1 in a certain place and a certain network.